STUDY OF THE POPULATION-II CEPHEID AU PEGASI

New photoelectric B and V observations of the Population II Cepheid AU Peg are presented. The available photometric measurements are collect ed from the literature and all data are analyzed with several period-f inding methods. The pe riod variation has been found to be non-linear, and between 1986 and 1990 the period increase stopped and seems to re verse. Since this Cepheid is a member of a binary system where proximi ty of the components is a deterministic factor, it is probable that th e pulsation is perturbed by the companion's tidal force. However, such a period variation can hardly be explained by tidal interaction alone . The surface brightness analysis resulted in new absolute parameters indicating that AU Peg is on the red edge of the instability strip.